Cardiac signal analysis may be performed by a variety of devices, such as implantable medical devices (IMDs) and external devices (e.g., smart watches, fitness monitors, mobile devices, Holter monitors, wearable defibrillators, or the like). For example, devices may be configured to process cardiac signals (e.g., cardiac electrograms (EGMs) and electrocardiograms (ECGs)) sensed by one or more electrodes. Features of cardiac signals may include the P-wave, Q-wave, R-wave, S-wave, QRS-complex, and T-wave. Accurate detection and delineation of features cardiac signals, such as T-waves, may be of importance for improving operation of devices.
Cardiac pacing is delivered to patients to treat a wide variety of cardiac dysfunctions. Cardiac pacing is often delivered by an IMD. An implantable cardioverter-defibrillator (ICD), for example, may provide pacing functionality and also provide cardioversion or defibrillation in response to detected cardiac tachyarrhythmias, if needed. However, pacemakers that do not provide anti-tachyarrhythmia shocks, and ICDs that do not deliver pacing therapy are also prevalent. An MD typically delivers such therapy to the heart via electrodes located on one or more leads, which may be intracardiac or extracardiovascular leads, although leadless IMDs for delivering such therapies have also been implemented. Furthermore, leaded and leadless cardiac monitors that do not deliver therapy have also been implemented.
Patients with heart failure may be treated with cardiac resynchronization therapy (CRT). CRT is a form of cardiac pacing. The ventricles of some heart failure patients contract in an uncoordinated, or asynchronous, manner, which greatly reduces the pumping efficiency of the ventricles. CRT delivers pacing pulses at particular times, e.g., atrioventricular (A-V) intervals and/or intra-ventricular (V-V) intervals, and particular locations, e.g., to one or both of the right and left ventricles, to re-coordinate the contraction of the ventricles. In some examples, CRT involves delivery of pacing pulses to both ventricles to synchronize their contraction. In other examples, CRT involves delivery of pacing pulses to one ventricle, such as the left ventricle, to synchronize its contraction with that of the right.